The present invention relates to sash locks in general, and in particular to a sash lock which is resistant to being forced open, and so to a method of locking sashes.
A common kind of sash lock cooperates with a keeper to tighten and lock a window. The keeper is mounted to one sash of a double-hung window. The sash lock has a rotatable cam mounted on a housing that is connected to the other sash of the window. Rotating the cam causes a finger which is part of the cam to move across the gap between the two sashes, engage a keeper mounted on the other sash and draw the sashes toward each other while forcing one sash up and the other down. This style of sash lock is common and quite old. It is also vulnerable to being forced open. In particular, it may be possible with some prior art sash locks to force a knife blade or similar tool into a crack between the two sashes, engage the cam with the blade, and force the lock to an open position.
It is an object of the present invention to reduce the chances of such a sash lock being forced open. To this end, the invention provides a sash lock with a rotatable cam to engage a keeper. The sash lock has a slide plate mounted below the cam. The slide plate is slidable between a retracted position in which its leading edge is withdrawn within the sash lock housing and substantially flush with the edge of the housing and an extended position in which the leading edge of the plate extends from the sash lock housing across the narrow gap between the sashes and into a slot in the keeper, so to prevent a knife blade from forcing the lock open. The slide plate is mounted for movement generally perpendicular to the edge of the sash, and it includes an arcuate recess in one side of the plate. The rotatable cam includes a pin which extends from the cam into the recess. When the cam is rotated, the finger moves, engaging the recess and forcing the slide plate to move outward into the gap between the sashes.
These and other features of the present invention will become clear from the following specification when taken together with the annexed drawings.